High-energy solid formulations, such as propellants, explosives, and gasifiers, generally consist of particulate solids, such as fuel material, oxidizers, or both, held together by an elastomeric binder. These formulations may also include a liquid plasticizer, such as a nitrate ester, which contributes to the elastomeric characteristics of the binder and adds additional energy to the formulation.
While the elastomeric binder matrix is an important means of dispersing and immobilizing the fuel material and oxidizer, the materials used in the binder burn with substantially lower energy than does the fuel material. The binder thus imposes a limit on the energy content available from the fuel material. One way to minimize this limitation is to use an elastomeric binder which releases as much energy as possible when burning with the fuel material. It is desirable, therefore, that the elastomeric binder have pendant groups which themselves are relatively high in energy.
Plasticizers are used in solid propellants and explosives to facilitate processing and increase flexibility and toughness, in addition to providing other benefits which vary with the nature and use of the formulation. Energetic or high-energy plasticizers are those that provide energy in addition to flexibility and toughness, and their inclusion therefore does not lessen the performance of the formulation. Considerations involved in the selection and use of plasticizers include compatibility with the other components of the formulation, including the primary energetic compounds and any binders present, the oxygen balance of the plasticizer, energy content, safety (i.e., stability with regard to detonation) and melting point. Plasticizers with melting points in a range which causes them to crystallize readily, for example, are of limited utility, since crystallization is detrimental to the plasticizer function and can adversely affect the mechanical properties of the propellant or explosive.
If a nitrate ester plasticizer is included in the formulation, it is desirable that the elastomeric binder be compatible with the nitrate ester plasticizer, i.e., nitroester-miscibility is required. If the binder system is insufficiently miscible with the nitrate ester plasticizer, the plasticizer will weep or flow and settle out from the binder. Certain polymers which have sufficiently high energies and would otherwise be useful elastomers for binders cannot be used in certain binder systems because they are incompatible or immiscible with the nitrate ester plasticizer. Polyethers prepared from tetrahydrofuran (THF) are examples of such polymers. These polyethers have sufficiently high energies, high load-bearing capabilities, and low glass transition temperatures (T.sub.g 's), but because they are immiscible with nitrate esters, they cannot be used in binder systems which utilize nitrate ester plasticizers. In addition to being high in energy, therefore, the polyethers and the elastomers formed therefrom should contain pendant groups which impart miscibility of the elastomers with nitrate ester plasticizers. Nitro, nitrato, nitroamino and cyano groups are examples of pendant groups which impart nitrate ester-miscibility to the polymer and have relatively high energies so as to contribute to the performance of the propellant.
In view of the foregoing, there exists a need for novel polyether polymers which, in addition to retaining the necessary characteristics of a binder, such as good elastomeric and strength characteristics, are sufficiently high in energy and sufficiently miscible with nitrate ester plasticizers.